1. Field of the Invention
The present invention relates to a focus detecting apparatus, particularly, relates to the focus detecting apparatus for performing automatically focusing on a designated surface of transparent substrates, such as a microplate and a slide glass in a microscope observation apparatus.
2. Description of the Related Art
In a field of biotechnology, in order to clarify reactions of various living cells under various conditions, a result of statistics analysis for many cells has been used in many cases frequently. For such purpose, conventionally, an apparatus so called as flow cytometer has been used. However, in recent years, a technique in which a result of the statistics analysis is obtained by acquiring images of many cells by a microscope observation apparatus and analyzing the acquired images has been used.
By the way, in order to examine actually the reaction of the living cell under various conditions, it is necessary to use, as objects of analysis, very many living cells cultured in a container such as a microplate. Accordingly, it is desired that as for a microscope observation apparatus for acquiring an image of a cell, it is constituted so that it may have an inverted microscope type optical arrangement, where observation is carried out from the lower part of a container such as a microplate, and further, a series of operations concerning capture of images such as change of a position of a view field, focusing, image acquisition, etc. is automated.
In automation of a microscope observation apparatus, an automation system for focusing is important particularly. Generally, as for the automation system for focusing, it can be divided roughly into two systems. One of the systems is called as active system in which an object (photographic object) is irradiated by illumination light such as infrared light, etc., and then a focus is detected by detecting an amount of the light, etc. Another system is called as passive system in which a focus is detected using an image captured through a lens.
However, in a microscope observation apparatus which acquires images of cell for investigating and clarifying a reaction of various living cells under various conditions, a focusing system of the active system having quick working speed has been adopted in many cases since it is necessary to acquire many images. As for a focus detecting apparatus that such active system is adopted, it is shown in Publication of the Japanese unexamined patent application, Toku Kai No. 2006-184777, for example.